1. Field of the Invention
The present inventions relates to traffic signals. More particularly, the present invention relates to power supplies for light emitting diode (LED) traffic signals.
2. Description of the Related Art
Traffic signal lamps typically use either incandescent or LED lamps. LED traffic signals are more reliable, more mechanically stable, safer, more energy efficient and more environmentally friendly than incandescent lamps. Thus, LED traffic signals are gaining in popularity.
LED traffic signals are typically used as a replacement for an incandescent bulb traffic signals. They may also be used in new traffic installations. Driven by stable current and voltage levels produced by switching power supplies, LED traffic signals consume relatively low amounts of power and have extremely long lifetimes compared to standard incandescent bulbs. Whether the signals is being retrofit into an existing traffic signal or is part of a new installation, the LED lighted traffic signals must meet governmental standards.
Governments regulate many aspects of the signal including chromaticity requirements, electromagnetic compatibility (EMC) requirements, controller capability requirements, sun phantom protection requirements, and photometric requirements such as dimming compatibility and brightness. However, there is no worldwide standard for traffic lights. Different requirements exist for the United States, for Europe and for Australia and New Zealand. Other differences include that the operating range of the Australia signal lamp is larger. Australian signals have a requirement related to the shape of the input current within ±500 microsecond of the peak input voltage. Australian traffic controllers utilize dimming in low light conditions. Preferably, linear dimming is utilized.
Further, because LED signals lamps are often retrofit into units originally housing incandescent traffic lamps, it is necessary to provide circuitry that is compatible with existing signals and that it mimics the way an incandescent signal behaves. A signal light that meets the governmental requirements and mimics the behavior of an incandescent signal is needed.